In French Patent No. 88 13 272, the Applicant describes apparatus for measuring the angle of rotation of a rotor of a motor relative to the stator thereof, which apparatus comprises 2n magnetic sensors disposed on a circumference that is fixed relative to the stator, n being the number of phases of the motor, each sensor comprising a magnetic circuit equipped with a transmission winding and a reception winding, the sensors being grouped together in pairs, the sensors in the same group being offset by 180 electrical degrees, the groups being uniformly offset from one another by a geometrical angle equal to k.360/2p, where k is an arbitrary number, and p is the number of pairs of poles of the motor, all the transmission windings being connected together in series and powered by an AC voltage lying in the range 2 kHz to 15 kHz, the reception windings in the same group of sensors being connected together in series, the envelope of the signals at the terminals of the sets of reception windings representing, to within one phase-shift, the image of the measurement of the angle of rotation of said rotor.
An embodiment of that sensor is described in detail in the French Certificate of Addition No. 89 10 533.
Such a sensor operates well but is relatively expensive to make, in particular for sensors used with motors having small numbers of poles (e.g. below six poles).
An aim of the present invention is to provide a sensor which costs less, in particular for sensors having small numbers of pairs of poles, while maintaining the same accuracy and the same operating safety.